Environmental drivers of
leaf litter decomposition in streams
Andreas Bruder1 & Julien Cornut2
[email protected]
1Institute
of Earth Sciences
of Applied
Microbiology
2Laboratory
food webs of forested streams
Aquatic hyphomycetes
Collectors/Filterers
Shredders
Aquatic
hyphomycetes
Shredders
Collectors/
Filterers
Predators
FPOM
Predators
leaf litter decomposition
Abiotic factors
Biotic factors
Litter mass remaining (%)
𝑴𝒕 = 𝑴𝟎 ∙ 𝒆−𝒌∙𝒕
Time (in days)
Time (in degree-days)
Bruder et al. (2014) Freshwater Biology
Biotic factors
Abiotic factors
> Temperature
> Litter characteristics
> Dissolved chemicals
> Biodiversity
> Pollution
> Community composition
> Flow velocity
>…
>…
role of abiotic conditions
VOSGES
decomposition rate k (d-1 K-1)
exponential decomposition rate k (d-1)
acidification
Cornut et al. (2012) Water Research
McKie et al. (2009) Oecologia
In this study, effects of acidification on fungal and shredder biomass was small
> but negative effects on their activity and in turn on decomposition
role of abiotic conditions
temperature and latitudinal gradient
(and decomposer groups)
Water temperature (°C)
+
Boyero et al. (2011) Ecology Letters
Dang et al. (2009) Ecology
Activity of fungi and shredders respond differently to temperature and latitude
> climate warming could change their relative importance for litter
decomposition and affect the carbon cycle
role
abiotic
conditions
Leaf of
litter
decomposition
flow velocity and fine sediment
Example from multiple stressor studies
200 -
Fungal mass (mg/g litter)
Leaf mass processed (%)
100 -
75 -
50 -
25 -
0-
Fast
150 -
100 -
50 -
0-
Slow
Flow velocity
Fast
Slow
Flow velocity
Outdoor/streamfed
N:
128
Area
0.045 m2
Discharge: 2 L·min-1
Volume:
3L
Sediment: 0.5 L
Res. Time: 75s
Bruder et al. (2016) Functional Ecology
Slow flow velocity reduces litter decomposition rate and fungal biomass
> situations comparable to littoral zones of forested lakes?
role
abioticeffects
conditions
Flowofvelocity
on benthic habitat
flow velocity and fine sediment
Measured flow velocity
Flow velocity effects on boundary layer
Boundary layer effects on
benthic habitat
Flow
Slow
Fluxes of oxygen,
nutrients, etc.
Fast
mod. from Stevens & Hurd (1997) Hydrobiologia
Fluxes = f(boundary layer thickness) = f(flow velocity)
Effects on physicochemical conditions in/on the sediment with
consequences on organisms and biological processes
role of biodiversity
leaf litter diversity (and biome effects)
Streams
Forest floors
decreasing latitude
<<
Species identity and environmental conditions dominate diversity effects
Handa et al. (2014) Nature
role of biodiversity
Decomposer diversity (and food-web complexity)
5 fungal spp.
1 fungal spp.
No fungi
Shredder richness
Both vertical and horizontal diversity influences litter decomposition rates
Jabiol et al. (2013) Journal of Animal Ecology
conclusions
Litter decomposition is sensitive to environmental conditions but:
> response depends on specific ecological and environmental situation
> can be different for the main decomposer groups (fungi vs shredders)
> depends on biodiversity but the picture is not very clear for aquatic situation
Part of ecological variation could be reduced using standardized substrate:
> for instance cotton strips (mainly cellulose)
> this approach is used in the ICP IM indicator Microbial Decomposition
but also in other global studies
(e.g. CELLDEX – testing decomposition in streams and riparian vegetation)
> results are transferable between studies using leaf litter and those using cotton
Thank you for your interest
and the Swiss Federal Office for the Environment (FOEN) for financial
support to participate at the ICP IM TF Meeting